JPH09294065A - Output buffer circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the power consumption of an output buffer circuit without increasing its starting time by performing the ON/OFF control of power supply of only the buffer circuit by a selection signal. SOLUTION: When a selection signal CTRL is high or released in an output buffer circuit 22, this high signal is inputted to one of both input terminals of an AND circuit. Then the oscillation signal sent from an oscillation circuit 20 and inputted to the other input terminal of the AND circuit is inputted to a 1st inverter circuit via the AND circuit and then outputted after undergoing the normal amplification and shaping via the 1st to 4th inverter circuits. When the signal CTRL is low, this low signal is inputted to one of both input terminals of the AND circuit. Then the oscillation signal sent from the circuit 20 and inputted to the other input terminal of the AND circuit is cut by this circuit. Thus, the function of the circuit 22 is stopped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a buffer circuit suitable for use in a temperature-compensated oscillator (TCO) which stabilizes the oscillation frequency of an oscillator against a change in ambient temperature by a compensation circuit, and more particularly to the above-mentioned TCO. The present invention relates to an output buffer circuit that can reduce power consumption without increasing startup time when it is integrated into an IC and downsized.

[0002]

2. Description of the Related Art Generally, there are various external factors that affect the frequency stability of an oscillator, but the most important factor in practical use is the temperature of the place where the oscillator is placed. A temperature-compensated crystal oscillator (TCXO) using a crystal oscillator will be described below as an example. That is, various methods have been proposed to eliminate the influence of the temperature,
One of them is a temperature-compensated crystal oscillator (TC) that stabilizes the oscillation frequency to a desired deviation with respect to changes in ambient temperature by changing the load capacitance of the crystal oscillator by a compensation circuit.
XO) is known. Conventional temperature-compensated crystal oscillator (T
As shown in FIG. 5A, a varactor diode (varicap) 2 is inserted in series with a crystal oscillator 3 and an amplifier 4, and a DC voltage generated by a compensation circuit 1 is applied to the varicap. It is applied. The capacitor 5 connected to the varactor diode 2 is
It is a capacitor for adjusting the control sensitivity (AFC sensitivity).

Further, the compensating circuit 1 is formed of a resistance circuit network including a plurality of thermistors R (T) and resistors R as shown in FIG. 5 (b), and the oscillation frequency of the crystal oscillator changes with temperature. DC voltage is generated so that the capacitance of the varicap cancels the change at each temperature. The compensating circuit 1 corrects variations in temperature characteristics of the crystal and variations in other circuit elements by replacing each circuit element of the resistance network with each product so that the frequency deviation is equal to or less than a frequency deviation specified in a desired temperature range. It is common to adjust so that
As the TCXO, as shown in FIG. 5, in addition to an indirect type in which a DC voltage change is simply generated by a thermistor and a compensating circuit such as a resistor, a parallel circuit of a thermistor and a capacitor is directly connected to a crystal oscillator in series. There is a direct type in which a high frequency current is directly connected to the compensating circuit, and the equivalent series capacitance is changed by changing the resistance of the thermistor depending on the temperature.

[0004]

In recent years, the TCXO has been widely used in communication devices such as mobile phones, and there has been an increasing demand for downsizing along with the downsizing of communication devices. Accordingly, the TCXO is also required to be further downsized. Therefore, it has been proposed to realize an epoch-making miniaturization and adjustment efficiency by mainly implementing the TCXO compensation circuit, but the following problems are not limited to the IC. was there. That is, at present, the wireless device using the TCXO is used by the customer to intermittently turn on / off the power for the purpose of extending the battery life, but this technique is effective for power saving. On the other hand, in order to turn off the entire power of the TCXO, when restarting, the oscillation start time after turning on the power is:
It had the drawback of having a few milliseconds. That is, TCX
The method of reducing the power consumption by turning on / off the entire O has a problem that it takes time to restart. On the other hand, the TCXO integrated into an IC has a characteristic that the current consumption of the circuit depends on the capacitance component included in the circuit load. That is, in the IC TCXO, the power of the output buffer circuit that drives the load circuit rather than the oscillation circuit is turned on / off.
When it is turned off, the transient current becomes large, and there is a fact that the current consumption for that is larger.

[0005]

[Object] The present invention has been made in view of the above circumstances, and has the same effect as when the power supply of an output buffer circuit is turned on / off without turning on / off the power supply of the buffer circuit. An object is to provide an output buffer circuit.

[0006]

To achieve the above object, the present invention cuts off the input of a signal to the output buffer circuit by a selection signal input at the input end of an output buffer circuit for amplifying and shaping an electric signal. A switch circuit is provided. Another feature of the present invention is that the output buffer circuit has a plurality of inverter circuits connected in series, and cuts off the inputs to the plurality of inverter circuits according to the selection signal input in a stage preceding the plurality of inverter circuits. That is, a logic circuit for

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on illustrated embodiments. FIG. 1 is a block diagram of a temperature-compensated crystal oscillator (TCXO) integrated into an IC having an output buffer circuit according to an embodiment of the present invention. As shown in FIG. 1, the TCXO includes an IC unit 10 having an IC having a compensation circuit unit and an oscillation circuit unit for generating a specific functional voltage with respect to a temperature axis, and the IC unit 10 described above.
The varicap portion 11 is externally connected to the varicap portion, and the crystal resonator 12 is connected to the varicap portion 11. The thermistor unit 13 of the compensation circuit
Is externally connected to the IC unit 10 and generates a DC voltage of a cubic function of temperature with a change in temperature. The IC unit 10 includes an input / output terminal group 14 for inputting / outputting various signals for adjusting and measuring temperature compensation.
A switching circuit 15 connected to the terminal group 14 and a memory (EE-PROM) 1 connected to the switching circuit 15
6 and a regulator 17 connected to the memory 16
A variable resistance network 18 connected to the switching circuit 15 and the memory 16, the thermistor section 13 and the varicap section 11, and a voltage dividing circuit 19 connected to the switching circuit 15 and the memory 16 and the varicap section 11. ,
An oscillation circuit 20 connected to the varicap portion 11,
The output buffer circuit 22 connected to the oscillation circuit 20 and the output terminal 21, the switching circuit 15 and the memory 1
6 and the power supply terminal 23 connected to the regulator 17,
And 24.

Next, the manufacturing process of the TCXO, particularly the outline of the adjustment will be described with reference to the operation flowchart of FIG. 2. First, in step 100, the temperature characteristic before compensation is measured. As a result of this measurement, frequency deviation data at each temperature is obtained, and the voltage division of the voltage dividing circuit 19 and the temperature characteristic of the variable resistance circuit network 18 are performed from the terminal group 14 to the memory 16 via the switching circuit 15. Regulator 17
The correction data including the correction of the output voltage variation is written (step 101). Next, in step 102, the compensation operation is actually operated to measure the output frequency at each temperature and the voltage of each part if necessary. As a result, if the temperature temperature characteristic of the frequency is within the specified value, the adjustment is ended, but if the standard value is not satisfied (NO in step 103), the correction data is further partially stored based on the measurement result. Write to 16 (step 104).
In the TCXO which has completed such adjustment, in the actual operation, the adjusted correction data is read from the memory 16, and the correction data is required to correct the variation in the temperature characteristic and the output voltage. The IC unit 10
It is sent to each section (the switching circuit 15, the regulator 17, the variable resistance circuit network 18, the voltage dividing circuit 19) therein. In addition, during use, the user may adjust the AFC sensitivity by the voltage dividing circuit 19.

Next, the output buffer circuit 22 which is the main part of the present invention will be described. FIG. 3 is a block diagram showing an embodiment of the present invention. The feature of the output buffer circuit 22 according to the present invention is that the output buffer circuit 22 is configured to have the same effect as the output buffer circuit 22 without turning on / off the power supply of the entire output buffer circuit 22. That is, as shown in FIG. 3, the output buffer circuit 22 includes the first, second, third and fourth inverter circuits 25, 2 connected in series.
An AND circuit 29 is provided in the preceding stage of 6, 27, 28, an oscillation signal from the oscillation circuit 20 is input to one input terminal of the AND circuit 29, and the AND circuit is input to the other input terminal of the AND circuit 29. The selection signal CTRL for turning ON / OFF the output of the signal to the output buffer circuit 22 is controlled by controlling the input terminal A (see FIG. 1). The first to fourth inverter circuits 25 to 28 are driven by the power supply VDD, and the output of the fourth inverter 28 is supplied to the output terminal 21.

Next, the operation of the output buffer circuit 22 will be described. As shown in FIG. 4, when the selection signal CTRL is a high signal or a release signal, the output buffer circuit 22 inputs the high signal to one input terminal of the AND circuit 29. The oscillation signal from the oscillation circuit 20 input to the other input terminal of the circuit 29 is input to the first inverter circuit 25 via the AND circuit 29 and the first to fourth inverter circuits 25 to 28. Then, it is amplified and shaped as usual and output (ON mode). Next, the selection signal CTRL
Is a low signal, the low signal is input to one input terminal of the AND circuit 29, and thus the oscillation circuit 2 is input to the other input terminal of the AND circuit 29.
The oscillation signal from 0 is cut off by the AND circuit 29, and the function of the output buffer circuit 22 is stopped (OFF mode). Therefore, as described above, the same effect as when the signal to the output buffer circuit 22 is turned ON / OFF by the selection signal CTRL from the input terminal A and the power supply of the output buffer circuit is ON / OFF controlled. can get. That is, the current consumption when a signal is not input to the buffer circuit is extremely small or zero, and when such a buffer circuit is used, the above-described effect can be obtained by turning on / off the input signal. In addition, in the above-described embodiment, an example in which the output buffer circuit having the amplitude limiting function is used in the TCXO integrated into an IC has been described. However, the present invention is not limited to this, and the output buffer circuit can be applied to various scenes. Needless to say.

[0011]

INDUSTRIAL APPLICABILITY As described above, the present invention provides TCXO.
Instead of controlling the ON / OFF of the entire power supply, the power of only the output buffer circuit is turned on by the selection signal CTRL.
Since the ON / OFF control is performed, the power consumption can be reduced without increasing the startup time.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of an integrated temperature compensation crystal oscillator (TCXO) having an output buffer circuit according to an embodiment of the present invention.

FIG. 2 is a flowchart of a method for adjusting the TCXO shown in FIG.

3 is an internal configuration diagram of the output buffer circuit shown in FIG. 1. FIG.

FIG. 4 is an ON / OFF state of the output buffer circuit shown in FIG.
It is an explanatory view of control operation.

FIG. 5A shows a conventional temperature-compensated crystal oscillator (TCX).
It is a basic block diagram of (O), (b) is a block diagram of a compensation circuit.

[Explanation of symbols]

1 ... Compensation circuit, 2 ... Varactor diode (varicap), 3, 12 ... Crystal oscillator, 4, 20 ... Oscillation circuit (O
SC), 10 ... IC section, 1
1 ... Varicap part, 13 ... Thermistor part,
14 ... Input / output terminal group, 15 ... Switching circuit,
16 ... Memory (EE-PRO
M), 17 ... Regulator, 18
... Variable resistance network, 19 ... Voltage dividing circuit,
21 ... Output terminal, 22 ... Output buffer circuit,
23, 24 ... Power supply terminals, 25, 26, 2
7, 28 ... First, second, third and fourth inverter circuits,
29 ... AND circuit, A ... Input terminal, 100-103 ... Each step,

Claims (2)

[Claims] 1. An output buffer circuit comprising an output buffer circuit which amplifies and shapes an electric signal, and a switch circuit which cuts off a signal input to the output buffer circuit by a selection signal input at an input terminal of the output buffer circuit. 2. The logic circuit, wherein the output buffer circuit has a plurality of inverter circuits connected in series, and cuts off inputs to the plurality of inverter circuits in accordance with the selection signal input at a stage preceding the plurality of inverter circuits. The output buffer circuit according to claim 1, further comprising: